1. Field of the Invention
The present invention relates to a direct mold clamping apparatus with an ejector, which is capable of uniformly applying a mold clamping force to a movable platen and is simple in construction and compact in size.
2. Description of the Related Art
Conventionally known direct mold clamping apparatuses include a push rod fixed to a movable platen, a ball nut attached to the rod so as to be rotatable and movable integrally with the rod and a ball screw mating with the nut. The ball screw is rotated in forward and reverse directions to reciprocate the movable platen, thereby effecting mold closing and mold opening operations. In apparatuses of this type, an ejector for ejecting moldings is attached to the movable platen in a manner such that the movable-platen-side end portion of the push rod is branched so that each branch end portion extends at a location outwardly of the ejector, and the extreme end of the branch end portion is coupled to its corresponding edge portion of the movable platen, to avoid interfering with the ejector. However, the distribution of a driving force applied to the movable platen through the branch end portions of the pusher rod is likely to produce irregular pressure force, so that the movable platen may possibly be deformed when it is subjected to a mold clamping force. In this case, a gap will be formed between a movable die and a stationary die at their contact faces, so that the moldings will be burred, for example. Thereupon, the movable platen is conventionally given a high rigidity such that it cannot be deformed even when it is subjected to an irregular mold clamping force. To attain this, however, the weight of the movable platen is increased thus requiring the use of a high-output drive source. As the moving speed of the movable platen is reduced, moreover, the required molding cycle time is inevitably lengthened. If the movable platen is bent as aforesaid, the movable platen rubs against its tie bars, thus creating friction loss and errors in control of the mold clamping force.
Furthermore, the mold clamping apparatuses with ejector are required to be simplified in configuration and made compact.